1. Field of the Invention
The present invention relates to a two cycle engine, and more particularly to a two cycle engine suitable for handheld power tools powered by an engine, such as a bush cutter, a chain saw, a blower or the like, and a tool using the engine.
2. Description of the Related Art
There have conventionally been known two cycle engines with improved outputs achieved by contrivance to the number and shape of their scavenge air passages or exhaust ports.
For example, a two cycle engine described in Patent Literature 1 is provided with, within its scavenge air passage, a straightening vane that divides the scavenge air passage into two in an upper-and-lower direction. The straightening vane directs air-fuel mixture flowing out of the upper opening of the scavenge air port by the air-fuel mixture flowing out of the lower opening so that the air-fuel-mixture flows from both openings flow in similar flow lines within a cylinder.
Patent literature 1: Unexamined Japanese Patent Application KOKAI Publication No. H08-296443
However, according to the two cycle engine of the patent literature 1, there is a disadvantage of undesirable gas mixture between the mixed gas in the cylinder and a combustion gas at the finish of one scavenging stroke from where the piston travels further to a top dead center. This undesirable mixture is caused by gas residue within the cylinder, resulting from ineffective scavenge of the combustion gas in the center portion of the cylinder, which is due to the straightening vane guiding the air-fuel mixture flowing out of the upper and lower openings of the scavenge air port toward an ignition plug through the inner wall surface of the cylinder at each scavenge stroke. Problematically, the undesirable gas mixture produces low concentration of the mixed gas that results in lowered output of the engine.